[NCLUG] Python v.s. Ruby, and PRNGs

[Jim Hutchinson]

On Thu, Apr 10, 2008 at 10:40 AM, Stephen Warren <swarren at wwwdotorg.org>
wrote:

> On Thu, April 10, 2008 9:46 am, Stephen Warren wrote:
> > On Wed, April 9, 2008 11:15 pm, Sean Reifschneider wrote:
> >> D1=`od --read-bytes=1 -t u1 /dev/random | head -1 | sed 's/.* //'`
> >> D1=$[(D1%6)+1]
> >
> > I think that'll introduce some slight bias in the results...
> >
> > The impact of this could be somewhat reduced by pulling 16-bit numbers
> > from /dev/random, to reduce the proportion of the range that's a
> "partial
> > die". Or, perhaps we could do the experiment with 8-sided dice, so mod
> 8.
>
> According to the last post here:
>
> http://www.unix.com/unix-dummies-questions-answers/34913-dev-urandom.html
>
> The correct way to fix this is:
>
>        bytes = self.f.read(2)
>        value = (ord(bytes[0]) << 8) | ord(bytes[1])
>        #roll = (value % 6) + 1
>        roll = int((value * 6) / 65536) + 1
>
> i.e. don't use modulus at all.
>
> I get the following results from 1000 runs of 10000 dice rolls using
> /dev/urandom on my probably-not-that-random machine:
>
> Min:   1.86
> Mean:  9.97
> Max:  29.92
> SD:    4.32
>
> So, also pretty variable, as expected, and pretty similar to the Python
> results.
>
> I wonder if /dev/random would be any different, but that's far too slow
> for me.
>
> (Anyway, this is probably getting a little off-topic. Let me know if
> anyone doesn't want to hear about this any more...)
>

I do. I find it interesting but you can mail me directly if others don't
want to hear. Would you be willing to share the code you used? I'd like to
explore it and try and learn more myself.

Thanks.
-- 
Jim (Ubuntu geek extraordinaire)
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